UP a creaky staircase above a pub in the heart of Hampstead is a room where some of the greatest poets, writers, actors and comedians have performed.

Unsurprising then that Pentameters Theatre, perched upon The Horseshoes pub in Heath Street, is regarded by many as a Hampstead institution.

This year as the theatre celebrates 50 years of putting on poetry, music and theatre, reflecting on the names that have made up its history is quite something.

Ted Hughes, Dannie Abse, Ivor Cutler, Roger McGough, Kingsley Amis, Rosemary Tonks, Edna O’Brien and Harold Pinter are just some of those that have graced its stage. The theatre also saw performers at the start of their careers including Rik Mayall, Ben Elton, French and Saunders, and Russell Brand. The celebrated producer Sonia Friedman credits her time working at Pentameters as inspiring her to make a career in theatre.

Founded and run by its artistic director Léonie Scott-Matthews, to walk into the 60-seater room is to enter into another world, a wonderland, of which Lewis Carroll would surely have approved.

Family photographs, old theatre bills and art work adorns the walls and among the comfy chairs there are dolls’ houses and cuddly toys and all sorts of ephemera.

“I never throw anything away,” says a bright-eyed Léonie, who can only sleep for two hours at a time. “It comes in handy as if we need a prop I usually have it!”

She bursts out laughing, something she does often. Regaling me with anecdotes and funny stories, with “oh, this will tickle you”. It would be hard not to be swept up by her energy. She paces the stage as she recalls the history of Pentameters, in a kind of one-woman show that she intersperses with impromptu performances of her poetry.

It was as a young woman in the 60s, living in Hampstead and attending the Royal College of Music on their speech and drama course that she happened on the idea of setting up a theatre in Hampstead.

Already a regular at The Rosslyn Arms (now no longer a pub), she had met her fair share of poets and writers. It was at this point that she realised she did not want to be an actor so decided to put on poetry nights.

First, however, she realised that in order to be alternative she had to prove to the establishment that she could do it their way. She edited poetry books, worked at the Poetry Society and won its gold medal for verse speaking.

And on August 7 1968 she turned a disused skittle alley in the basement of The Freemason’s Arms on Downshire Hill into a vibrant and bustling venue for £1 a week rent.

“Quite often writers who were known for other stuff wanted to perform their poetry,” she says citing the famous psychiatrist RD Laing’s challenging 45-minute performance of his sonnets.

“No one dared leave!”

Then there was the time Léonie struck up a conversation with a young man at the Haverstock Arms and suggested he do something at Pentameters.

The mysterious man was in fact Harold Pinter and he would go on to perform at Pentameters in his play The Dumb Waiter.

In the summer of 1970 Pentameters was briefly an open-air venue. Then from 1970 to 1971 it was at the Haverstock Arms. The theatre found its final “home” at The Three Horseshoes pub, now The Horseshoes.

“This is like my home,” she says lovingly of the intimate space. “People love it here because of the ambience, it has character.”

The venue puts on some 14 plays a year and these can be new plays (Léonie reads “hundreds of scripts”) as well as revivals.

There is a Sunday night and open mic night where her partner, Godfrey, and other musicians can come and perform and jam. The theatre is independent and has never relied on grants.

Léonie and Godfrey are quite a formidable team.

She greets guests individually at the box office before the play and Godfrey designs all of the production posters and T-shirts.

Her daughter with Godfrey, Alice Old, is a performer and has a band, The Butterfly Wheel. Léonie admits that she has now come to terms with the fact that her son, Durrell Scott-Cooper, who went missing in 2003 when he was 25, may never return.

“I may never know in my lifetime but that is the power’s choice,” she says. “You can’t have everything. I have an amazing partner, a wonderful daughter, a great home and love my life and I want it to go on.

“I don’t yearn for anything.”

Indeed, she is already putting together a book on Pentameters and hopes to publish a collection of her poetry.

“There is great longevity in my family and I’m now planning for the next 25 years of Pentameters,” she says with a flourish. “I have the most wonderful life. I live very simply but I love what I do.”